1. Field of Invention
The present invention relates to a field of integrated circuits, and more particularly to a high-frequency bandwidth amplifying circuit.
2. Description of Related Arts
For the various signal receivers in fields of RF communications, optical fiber communications and high-speed serial communications, it is required to amplify the received weak signals before the subsequent treatment. Along with the gradually increased signal frequency, loss of the high-frequency signals during the transmission in the medium gradually increases. As is known to the one skilled in the art, the higher frequency the signals have, the higher bandwidth the amplifying circuit is required to have; the higher loss the signals have, the higher gain of the amplifying circuit is required to have, so that the amplifier is required to have bigger and bigger gain-bandwidth product.
Referring to FIG. 1, a conventional high-frequency bandwidth amplifying circuit is shown. The conventional high-frequency bandwidth amplifying circuit comprises an operational amplifier which comprises a first FET M1 and a second FET M2, wherein a gate electrode of the first FET M1 and a gate electrode of the second FET M2 are connected to an external input terminal IN; a source electrode of the first FET M1 is connected to an external power supply VDD; a source electrode of the second FET M2 is connected to ground; a drain electrode of the first FET M1 and a drain electrode of the second FET M2 are both connected to an output terminal OUT, in such a manner that, via the output terminal OUT, the operational amplifier outputs the amplified high-frequency signal which is inputted by the external input terminal IN. When the operational amplifier is amplifying the inputted high-frequency signals, because of the parasitic capacitor of the first FET M1 and the second FET M2, the high-frequency signals introduce a pole on the transmission channel and the high-frequency signal transfer function decreases 20 db/10 octave at the pole, so as to reduce the bandwidth of the high-frequency signal transfer function decreases. As is known to the one skilled in the art, the amplifier (the operational amplifier) only amplifies the high-frequency signals within the bandwidth; the lower bandwidth, the weaker amplification the amplifier applies on the high-frequency signals. Thus, for the high-frequency bandwidth amplifying circuit, it is necessary to possibly minimize the parasitic capacitor to reduce the effects thereof on the frequency of the high-frequency signals. According to prior arts, the amplifiers usually have small sizes for reducing the parasitic capacitor, but the small-sized amplifiers have a poor current driving ability and thus fail to satisfy working requirements.
Besides, based on the above content, a higher gain bandwidth product can be obtained via providing higher currents and higher power consumption because the gain bandwidth product is directly proportional to a square of the working current. However, the manner is becoming less attractive because the manner needs the relatively high current and also the relatively large power consumption. Along with the further increased requirement of the gain bandwidth product for the high-frequency bandwidth amplifying circuit, further increased currents are no longer able to bring effective increase in the gain bandwidth product because of the restriction of the conventional topological structure, so that the improvement in the gain bandwidth product of the high-frequency bandwidth amplifying circuit hits the bottleneck.
Thus it is necessary to provide an improved high-frequency bandwidth amplifying circuit to overcome the above disadvantages.